Method for operating a hot blast stove

ABSTRACT

A method for operating a hot blast stove in which a combustion gas of a sulfur-containing fuel is passed through a regenerator to heat up the regenerator and air subsequently is blown through the regenerator and is heated by heat-exchange with the heat built up in the regenerator, the improvement comprising preheating the air to a temperature above the acid dew point of the combustion gas whereby corrosion of the regenerator by sulfur is prevented.

United States Patent Higashi Sept. 2, 1975 [75] Inventor: MasaruHigashi, Hitachi. Japan [73] Assignee: Nippon Mining Co., Ltd., Tokyo.

Japan [22] Filed: June 12, 1974 [21] Appl. No.: 478,499

[52] US. Cl 432/30; 432/214 [51] Int. Cl. F2411 7/00 [58] Field ofSearch 432/30, 214, 217, 218

[56] References Cited UNITED STATES PATENTS 1,880,229 10/1932 Andrews cta1 1. 432/30 2,171,596 9/1939 Parker 432/30 X 3.061.292 10/1962 Kinncy432/30 Primary E \'uminer.lohn J. Camby Attorney, Agent, orFirm-Sughrue, Rothwell, Mion, Zinn and Macpeak 5 7 ABSTRACT A method foroperating a hot blast stove in which a combustion gas of asulfur-containing fuel is passed through a regenerator to heat up theregenerator and air subsequently is blown through the regenerator and isheated by heat-exchange with the heat built up in the regenerator, theimprovement comprising preheating the air to a temperature above theacid dew point of the combustion gas whereby corrosion of theregenerator by sulfur is prevented.

4 Claims, N0 Drawings METHOD FOR OPERATING A HOT BLAST STOVE BACKGROUNDOF THE INVENTION 1. Field of the Invention g This invention relates to amethod for operating a hot blast stove in which a sulfur-containing fuelis burned.

with the heat of the combustion gas being stored in-a regenerator, andwith the air to be heated by the regenerator being brought into contactwith the regenerator for heat exchange. More specifically. thisinvention relates to a method for operating a hot blast stove withoutcausing corrosion of the regenerator structure.

2. Description of the Prior Art It is customary to introduce a hot blastinto a smelting furnace in order to smelt ores. Various methods areavailable to generate heat for the hot blast. Generally, however. priortechniques have employed a method in which an iron blast furnace gas isused, or a method in which a fuel is burned and the sensible heat of theexhaust gas is utilized. The sensible heat of the exhaust I gas isstored generally in a heat-receiving device constructed of bricks, bypassing the exhaust gas through the heat-receiving device. Thisheat-receiving device is generally called a regenerator. ln operation,when the temperature of the regenerator has reached a fixed level, theflow of the combustion gas is stopped, and then air is blown in anopposite direction to the combustion gas flow, so that air is heatedwith the heat stored in the regenerator. As a result of this operationair is heated to a fixed temperature and usually. all of this equipmentis called a hot blast stove.

Thus, in a hot blast stove operation. a fuel is burned in a combustionfurnace which is separate from a regenerator, and then, the combustiongas is passed through the regenerator to transfer the heat of thecombustion gas to the regenerator, with the combustion gas being passedthrough the regenerator for about 30 to 55 minutes to achieve a walltemperature of about 250 to 350C. Then, in order to use the stored heatfor a desired purpose, air at room temperature is introduced into theregenerator generally from the side of the outlet of the combustion gasfrom the regenerator and is brought into contact with the regenerator torecover the heat as hot blast. In this case, the temperature of thesection of the regenerator near the air inlet of the regenerator dropsto about 50C.

However, in such a method for operating a hot blast stove, a sulfur freeheat source is required. When the sulfur content of the fuel is lessthan 0.2 percent, S which is a main cause of corrosion is scarcelyformed, and therefore, no consideration on the corrosion of the stovedue to the sulfur is needed. However when the sulfur content is higher,corrosion of the regenerator in contact with the combustion gas occurs,and the regenerator can be damaged or destroyed.

It is said that when a heavy oil containing 2% of sulfur is used as afuel, the amount of corrosion of a steel material in general. forexample, is to 50 mg/dm Hr. If the lifetime of a hot blast stove can becalculated on this basis, a hot blast stove should be renewed everyeight years when it is operated in the conventional method. This isabout half of the inherent lifetime. Generally speaking. the inherentlifetime of a hot blast stove is about yearsv In order to avoid this,fuels containing large quantities of sulfur have not been employed as aheat source.

SUMMARY or THE- INVENTION Accordingly, .it is an object of thisinvention to remove these defects of the conventional methods, and toprovide a method for operating a hot blast stove which permits the useof a fuel having a high sulfur content which could not be usedpreviously.

The present invention provides a method for operating a hot blast stoveof the type in which a combustion gas of asulfurcontaining fuel ispassed through a regenerator and the regenerator heated up, followed bythe blowing of air through the regenerator to heat the air using theheat built up in the regenerator, comprising preheating the air to beblown through the regenerator to a temperature above the acid dew pointof the combustion gas prior to blowing the air through the regenerator.

DETAILED DESCRIPTION OF THE INVENTION According to this process, the hotblast stove is operated so that the temperature of every part of theregenerator is not below the acid dew point of the combustion gas. Inorder to achieve this, the air to be blown for about 35 to 60 minutesthrough the regenerator, generally at 500 to 650 Nm"/min, for producingthe hot blast is pre-heated toa temperature above the acid dew point.preferably at least about C above the acid dew point, so that uponblowing the pre-heated air through the regenerator, the temperature ofthe regenerator is maintained always at a temperature above the acid dewpoint.

The range of acid dew point of the exhaust gas can not be unequivocablydefined. The acid dew point is dependent upon the sulfur content of thefuel, and the water content in the exhaust gas. Therefore, the heatingtemperature for the blast air is determined by the fuel used. Generally,a pre-heating temperature of about 200C to about 250C is sufficient. Thepreheating of the air blast can be by any known method, but a method forheating using steam, or a method of heating by circulating a part of thehigh temperature hot blast is preferred.

The following example illustrates the method of this invention morespecifically. Unless otherwise indicated all parts, and percents are byweight.

EXAMPLE A hot blast stove which was used to provide a feed hot blast toa smelting furnace for smelting a copper ore and which had aregenerating capacity of 6,700,000 Kcal per hour was used. A heavy oilcontaining 2 percent of sulfur was burned at a rate of 1,000 liters perhour, and the burning was stopped when the temperature of the brick atthe outlet of the combustion exhaust gas of the hot stove reached 350C.After regeneration, using a heat exchanger separately provided, air waspre-heated to 200C with superheated steam, and then fed to the hot blaststove at a rate of 500 Nm per minute. The supply of the blast wasstopped when the hot blast temperature fed to the smelting furnace couldnot be maintained at 900C, and the operation was switched over to onefor regeneration. The time required for regeneration was about minutes,and the time for supplying the hot blast was about minutes. Theseoperations were repeated alternately. After a lapse of about 6 months,scarcely any appreciable corrosion or damage of the stove was observed.

Since the damage of the regenerator by corrosion can be prevented byoperating the hot blast stove in accordance with the method of thisinvention. fuels having a slightly higher sulfur content, e.g., up toabout 3 percent and higher as desired, can also be utilized. Thus,

use of such a higher sulfur content has not been possible with priorapproaches as set forth above. The shortened lifetime of the stove,estimated at about 8 years in the conventional method, can be obviated.Rather, since the pre-heating of air to be supplied also causes adecrease in the periodical change in thermal expansion, it is expectedthat the brick collapsing of the hot blast stove due to thermal stresseson the brick can be prolonged.

Furthermore, because of the air pre-heating, the regenerator can beheated to the desired temperature even if the combustion time is shorterthan in conventional method.

While the invention has been described in detail and with reference tospecific embodiments thereof, it will be apparent to one skilled in theart that various changes and modifications can be made therein withoutdeparting from the spirit and scope thereof.

What is claimed is:

l. A method of operating a hot blast stove of the type in which acombustion gas of a sulfur-containing fuel is passed through aregenerator to transfer the heat of the combustion gas to theregenerator, and subsequently air is blown through the regenerator toheat the air and utilize the heat stored in the regenerator, theimprovement comprising pre-heating the air to be passed through theregenerator to a temperature above the acid dew point of said combustiongas prior to blowing the air through the regenerator, said pre-heatingtaking placing by recirculating a portion of the air passed through theregenerator.

2. The method of claim 1, wherein said pre-heating is to a temperatureof at least about 200C.

3. The method of claim 1, wherein the passing of combustion gas throughthe regenerator and the passing of air is conducted alternately.

4. A method for operating a hot blast stove of the type in which acombustion gas of a sulfur-containing fuel is passed through aregenerator to transfer the heat of the combustion gas to theregenerator and subsequently air is blown through the regenerator toheat the air and utilize the heat stored in the regenerator, theimprovement comprising pre-heating the air to be passed through theregenerator to a temperature above the acid dew point of said combustiongas prior to blowing the air through the regenerator, said preheatingtaking place by using steam.

UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTION QPATENT NO. 3, 902, 844

DATED September 2, 1975 INVENTOR(5) I Masaru HIGASHI It is certifiedthat error appears in the abcve-identified patent and that said LettersPatent q are hereby corrected as shown below:

IN THE HEADING: I

The CTaimed Priority Data was omitted: Should read; --June 12, 1973Japa.n----'-----65363/73 Signed and Sealed this twenty-fourth Day ofFebruary 1976 Q [SEAL] Arrest: i r RUTH c. MASON c. MARSHALL DANNAIM-Wing ff ('mnmissiuru'r uj'Parenrs and Trademarks

1. A method of operating a hot blast stove of the type in which acombustion gas of a sulfur-containing fuel is passed through aregenerator to transfer the heat of the combustion gas to theregenerator, and subsequently air is blown through the regenerator toheat the air and utilize the heat stored in the regenerator, theimprovement comprising pre-heating the air to be passed through theregenerator to a temperature above the acid dew point of said combustiongas prior to blowing the air through the regenerator, said pre-heatingtaking placing by recirculating a portion of the air passed through theregenerator.
 2. The method of claim 1, wherein said pre-heating is to atemperature of at least about 200*C.
 3. The method of claim 1, whereinthe passing of combustion gas through the regenerator and the passing ofair is conducted alternately.
 4. A method for operating a hot blaststove of the type in which a combustion gas of a sulfur-containing fuelis passed through a regenerator to transfer the heat of the combustiongas to the regenerator and subsequently air is blown through theregenerator to heat the air and utilize the heat stored in theregenerator, the improvement comprising pre-heating the air to be passedthrough the regenerator to a temperature above the acid dew point ofsaid combustion gas prior to blowing the air through the regenerator,said pre-heating taking place by using steam.